Polyester resins have been prepared in the past by reacting such carboxylic acids as diglycolic acid with a dihydric alcohol such as a glycol but these polyester resins of the prior art were comparatively low molecular weight materials such as those having a molecular weight of about 3,000 to about 8,000 and many had an inherent viscosity of only about 0.25. These low molecular weight polyesters of diglycolic acid and glycols were not capable of forming self-supporting films and had been suggested for use as a propellant plasticizer, among other things. The Casey and Gleckler applications referred to hereinabove produce polyester resins from diglycolic acid and an unhindered glycol which have a molecular weight sufficiently high so as to provide a polymeric material possessing self-supporting, film-forming properties. Those polyester resins are normally solid, biodegradable, hydrolyzable polyester resins.
Polyglycolic acid is sometimes referred to as polyglycolide and sometimes referred to as polyhydroxy acetic ester. The polyglycolic acid has been a known material for a plurality of years and is known to be capable of forming self-supporting films and orientable fibers, which have found application as bioabsorbable surgical sutures. When any oriented monofilament is made from a polymeric material of sufficiently high molecular weight, of significant thickness, so as to provide the desired tensile strength, the monofilamentary material has a tendency to be stiffer than desired by some surgeons. It is known that stiffness in a filament varies as the 4th power of the diameter of the filament. However, when one combines chemically a high molecular weight polyglycolic acid composition with a polyester of diglycolic acid and an unhindered glycol, the resultant polymeric reaction product can be extruded into a monofilamentary material with significantly enhanced flexibility while still retaining its tensile strength.